The invention relates generally to the field of fluid flow measurements. More specifically, the invention relates to an apparatus and method of rapidly determining viscosity of a low viscosity fluid, such as an ink jet printing ink formulation.
The need for rapid measurement of viscosity of low viscosity fluids has recently arisen in the context of ink jet printing ink formulation where the additional complication of opacity excludes volumetric capillary systems with optical detection. In the development of ink jet printing inks there is the need for expedient viscosity measurement of numerous samples in the range from 1-20 cp. This range is most conveniently accessed by standard capillary methods. Existing devices use time elapsed during efflux of a fixed volume of fluid, typically relying on optical detection of the meniscus of the sample fluid as it passes through the capillary. Since ink jet printing inks are typically opaque and of low surface tension, such devices and methods are inapplicable as very small amounts of residual fluid can obscure the passing of the meniscus. Other devices and methods exist for detecting the meniscus of the fluid, such as thermal conductivity. These devices and methods, however, are known to inflate the price of the fluid measurement process. Hence, their routine use among many laboratory sites would not be cost effective. Additionally, the accuracy provided by such instruments exceeds that which is necessary for many industrial applications.
Therefore, a need persists in the art for an apparatus and method for rapidly measuring the viscosity of low viscosity fluids, such as ink jet printing ink formulations, that is easy to construct and use.
It is, therefore, an object of the invention to provide an apparatus for rapidly measuring viscosity of a low viscosity fluid.
Another object of the invention is to provide an apparatus for measuring viscosity of fluids having a viscosity in the range from 1 cps to about 20 cps.
Yet another object of the invention is to provide a method of rapidly measuring the viscosity of a fluid by mass flow rate.
The present invention is directed to achieving one or more of the objects, features and advantages set forth herein. Briefly summarized, according to one aspect of the present invention, an apparatus for measuring viscosity of a fluid has a tube for sampling a fluid. The tube has a fluid inlet orifice and a fluid outlet orifice. A fluid sample container is arranged beneath the tube for receiving a fluid sample exiting the fluid outlet orifice of the tube. The fluid sample container is supportedly arranged on a balance that determines weights of the fluid sample container during fluid sampling. A data processing device, such as a computer, operably connected to the balance records and processes sequential weights of the fluid sample container during fluid sampling. The computer incorporates a computer readable program for enabling the computer to receive a plurality of signals representing the sequential weights of the fluid sample container. The computer then determines the viscosity of the fluid sample based on this plurality of signals.
In another aspect of the invention, a method of measuring viscosity of a fluid comprises the step of introducing a fluid sample into an elongated, narrow tube. The temperature of the fluid sample flowing through the elongated tube is maintained and controlled by a temperature barrier layer arranged about the tube. Fluid flowing through the tube passes into a sample container supported on a digital balance that enables a determination of a plurality of weights of the fluid sample. The plurality of weights of the fluid sample is then converted into a measure of viscosity of the fluid sample.
The present invention has numerous advantages over existing developments including: it produces rapid viscosity measurements of low viscosity fluids; and, it is simple to use and cost effective to manufacture.